/******************************************************************************
 * Copyright (C) 2014 ShenZhen YiHua Computer Co., Ltd.
 * All Rights Reserved.
 * 本软件为深圳怡化电脑股份有限公司开发研制。未经本公司正式书面同意，其他任何个人、团体
 * 不得使用、复制、修改或发布本软件.
 *****************************************************************************/
package net.dgg.dggcloud.core.util;

import java.net.InetAddress;
import java.net.UnknownHostException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.security.SecureRandom;
import java.util.Random;

public class RandomGUID {

    private static String valueBeforeMD5 = "";

    private static String valueAfterMD5 = "";

    private static Random myRand;

    private static SecureRandom mySecureRand;

    private static String strId;

    private static final int PAD_BELOW = 0x10;

    private static final int TWO_BYTES = 0xFF;

    static {
        mySecureRand = new SecureRandom();
        long secureInitializer = mySecureRand.nextLong();
        myRand = new Random(secureInitializer);
        try {
            strId = InetAddress.getLocalHost().toString();
        } catch (UnknownHostException e) {
            e.printStackTrace();
        }
    }

    private RandomGUID() {
    }

    public static String nextGUID() {
        return nextGUID(false);
    }

    public synchronized static String nextGUID(boolean secure) {
        getRandomGUID(secure);
        String raw = valueAfterMD5.toUpperCase();
        StringBuffer sb = new StringBuffer(64);
        sb.append(raw.substring(0, 8));
        sb.append("-");
        sb.append(raw.substring(8, 12));
        sb.append("-");
        sb.append(raw.substring(12, 16));
        sb.append("-");
        sb.append(raw.substring(16, 20));
        sb.append("-");
        sb.append(raw.substring(20));

        return sb.toString();
    }

    private static void getRandomGUID(boolean secure) {
        MessageDigest md5 = null;
        StringBuffer sbValueBeforeMD5 = new StringBuffer(128);

        try {
            md5 = MessageDigest.getInstance("MD5");
        } catch (NoSuchAlgorithmException ex) {
            throw new java.lang.RuntimeException("ʵ��MessageDigestʱ����.", ex);
        }

        try {
            long time = System.currentTimeMillis();
            long rand = 0;

            if (secure) {
                rand = mySecureRand.nextLong();
            } else {
                rand = myRand.nextLong();
            }
            sbValueBeforeMD5.append(strId);
            sbValueBeforeMD5.append(":");
            sbValueBeforeMD5.append(Long.toString(time));
            sbValueBeforeMD5.append(":");
            sbValueBeforeMD5.append(Long.toString(rand));

            valueBeforeMD5 = sbValueBeforeMD5.toString();
            md5.update(valueBeforeMD5.getBytes());

            byte[] array = md5.digest();
            StringBuffer sb = new StringBuffer(32);
            for (int j = 0; j < array.length; ++j) {
                int b = array[j] & TWO_BYTES;
                if (b < PAD_BELOW) {
                    sb.append('0');
                }
                sb.append(Integer.toHexString(b));
            }

            valueAfterMD5 = sb.toString();

        } catch (Exception ex) {
            ex.printStackTrace();
        }
    }

}
